Re: pg_stat_io clarifications: background worker, writes and reads - Mailing list pgsql-general

Hello list,

what is the "background worker" in the pg_stat_io statistics view? I'm
reading the documentation but can't figure this one out knowing that it is
not autovacuum or bgwriter. And I'm not aware of any extension I might
have with registered background worker.

Additionally, how can it be evictions > writes? I would expect every
eviction to cause a write.

Finally about "hits", I understand they are reads found in shared_buffers,
so they never registered into the "reads" counter. So is "reads" in
pg_stat_io the equivalent to misses, i.e. the opposite of "hits", the read
attempts not found in the shared_buffers, that needed to be fetched from
the disk (or OS buffercache)?

    backend_type    |    object     | context |  reads  |  read_time  | writes | write_time | writebacks | writeback_time | extends | extend_time | op_bytes |   hits    | evictions | reuses | fsyncs | fsync_time |          stats_reset
-------------------+---------------+---------+---------+-------------+--------+------------+------------+----------------+---------+-------------+----------+-----------+-----------+--------+--------+------------+-------------------------------
  background worker | relation      | normal  | 5139575 | 2196288.011 |  63277 |    1766.94 |          0 |              0 |       0 |           0 |     8192 | 876913705 |   5139653 |        |      0 |          0 | 2024-04-08 08:50:02.971192+00


Thank you in advance,
Dimitris